1. Field of the Invention
The present invention relates to an engine system.
2. Description of Related Art
Since automobiles using a gasoline as a fuel emit carbon dioxide (CO2), hydrogen has attracted attention as an alternative fuel. However, hydrogen is a flammable substance and has a high explosibility and caution is required when hydrogen is stored or reserved.
Prior arts for solving this problem are disclosed in Document 1 (Japanese Patent Laid-open No 2005-299499) and Document 2 (Japanese Patent Laid-open No 2005-147124). Documents 1 and 2 disclose means for reserving hydrogen as a hydrogenated fuel and taking out hydrogen gas utilizing a chemical reaction and supplying the hydrogen gas to an automobile when the hydrogen is required.
Document 1 discloses a hydrogen-used internal combustion engine for enhancing a reaction efficiency to increase a quantity of produced hydrogen when a dehydrogenation reaction is caused utilizing energy of exhaust gas and for simply constructing a mechanism for causing the dehydrogenation reaction. The hydrogen-used internal combustion engine includes a casing which is disposed inside an exhaust passage of the internal combustion engine and an end of which is disposed outside the exhaust passage, a catalyst disposed in the casing, a fuel supplying means for supplying a fuel containing an organic hydride, and a hydrogen supplying means for supplying the internal combustion engine with hydrogen taken out of the fuel containing the organic hydride by the dehydrogenation reaction on the catalyst.
Document 2 discloses a hydrogen-used internal combustion engine for providing a system in which one or two or more kinds of fuel can be freely selected and supplied. This hydrogen-used internal combustion engine is supplied with one or more kinds of fuel selected from a group of a hydrogenated fuel, a dehydrogenation product obtained by dehydrogenating the hydrogenated fuel and hydrogen, and is thereby operated. The hydrogen-used internal combustion engine includes a hydrogenated fuel reservoir portion, a reacting means for causing dehydrogenation reaction, a separating means for separating hydrogen-rich gas from a dehydrogenation product, and a dehydrogenation product reservoir portion for reserving a dehydrogenation product.
Documents 1 and 2 disclose that the hydrogenated fuel is poured into a reactor vessel containing a catalyst to obtain hydrogen. Since the dehydrogenation reaction of the hydrogenated fuel used here is an endothermic reaction, it is required to supply heat to the reactor vessel. In general, heat of the exhaust gas from the engine is utilized.
A possible method for reducing a volume of the reactor vessel is such that a hydrogen medium is heated to a reaction temperature and vaporized using a vaporizer and then supplied to the reactor vessel.
However, this method involves a problem. The operating state of the engine constantly varies and thus an amount of supplied heat is varied. At this time, a boiling position of the hydrogen medium in the vaporizer is constantly shifted forward and backward. Therefore, it is difficult to fix a shape of a hydrogen medium flow path in the vaporizer either for gas or for liquid and there is no other choice but to use an inefficient heat exchanger both for gas and for liquid.
It is an object of the present invention to provide an engine system using a small-sized heat exchanger having a high efficiency and a stable performance for heating and vaporizing the hydrogen medium supplied to the reactor vessel.